Method of bleaching textile



Nov. 24,1942. BURKHQLDER 2,302,936

METHOD OF BLEACHING TEXTILE MATERIALS Filed March 2, 1940 3 Sheets-Sheet l Wu uu zz Bnvcntor ALDEN HBURKHOLDER a 2 E Gttorncg Nov. 24, 1942. BURKHQLDER 2,302,936

METHOD OF BLEACHING TEXTILE MATERIALS Filed March 2, 1940 3 Sheets-Sheet 2 \s 67 47 n a 45 42 Is. 44 58 l: m D

I 49 A D 5 g 60 m (6 63 V 6 3nnentor ALDEN H. BURKHOLDER attorney 1942- A. H. BURKHQLDER 2,302,936

METHOD OF BLEACHING TEXTILE MATERIALS Filed March 2, 1940 3 Sheets-Sheet 3 FIG. 4 39 39 59 $9 Ennentor t t ALDENHDURKHOLDER F/zn Ottorneg Patented Nov. 24, 1942 UNITED STATES PATENT OFFICE 6 Claims. (Cl. 8-108) This invention relates to the bleaching of textile materials; more particularly. to methods of bleaching fibers, threads, fabrics or the like. Cotton and other materials of natural origin may be bleached according to the teachings of the 'invention, but it is in the bleaching of materials of regenerated cellulos that the invention may be employed to the greatest advantage. As hereinafter explained, the invention is especially useful in the continuous processing of viscose artificial silk thread.

Textile materials are usually subjected, at some stage in the processing thereof, to the action of a bleaching agent, for the color of the unbleached material is objectionable for many uses. In the case of unbleached cellulose, the objectionable color is usually attributable to the presence of complex organic impurities many of which are eliminated or otherwise rendered innocuous by the use of bleaching agents which are known to have an oxidizing action. Such bleachingagents v include not only chlorine but also solutions of potassium chlorite, sodium chlorite, sodium hypo- .chlorite, sodium hypobromite, calcium hypoof its efficiencv, is dependent upon the amount of its available chlorine. The latter factor is an arbitrary measure of its bleaching power, this even though the bleach ng agent contains a substance other than chlorine as the principal bleaching constituent. Solutions of sodium hypochlorite, which are particularly effective in this respect, are widely used as bleaching agents; however, the other substances already mentioned may also be employed.

In general, the activity of a given bleaching solution may be regulated by varying such factors as its pH value, concentration, temperature, etc., as well as by controlling the length of time during which it is applied. Heretofore. it has been usual to maintain such bleaching solutions at a pH value substantially greater than '7: indeed, definite alkalinity has been thought to promote stability of the solution. The present invention, on the other hand. provides a method of bleaching pursuant to which the material to be bleached is subjected to treatment with a bleaching solution having a pH of substantially 7, preferably for a relatively short period of time.

bleaching solution is more fully described hereinafter.

Following bleaching operations carried out in .the ordinarymanner, it has been customary to treat thebleached material with an antichlor to arrest the action of any bleaching solution re maining therein; otherwise, such excess bleaching solution might continue to act upon the material to such an extent as to damage it. Notwithstanding the fact that it has long been desired to dispense with the use of an antichlor in order that the time and cost involved in applying it might be saved, its use has heretofore been regarded as inescapable. The present invention successfully eliminates the antichlor even under conditions in which its use has been considered to be indispensable.

The facility with which the present invention may be employed renders it particularly adaptable to the continuous processing of thread or the like. In such a process, it is desirable to process substantially continuous lengths of thread on apparatus generally similar to that shown, described and claimed in application Serial No. 7,114, filed February 18, 1935, by W. F. Knebusch and A. H. Burkholder (Patent 2,225,642) The invention provides a novel method of bleaching regenerated cellulose thread while it is continuously but temporarily stored in the form of an advancing helix characterized by a large number of closely spaced turns, the thread being treated while in this form with a bleaching solution containing a strong-acid-neutralized oxy-halogen salt of an alkali or alkaline-earth metal; the thread is thereafter washed without the use of an antichlor and subsequently dried.

For convenience, the invention will be described as employed in continuous processing of multiple filament viscose artificial silk thread.

In the drawings, Figure 1 represents a vertical sectional elevation of one form of apparatus for the manufacture of viscose artificial silk thread by a continuous process in connection with which the present invention may be employed. Figure 2 is an end elevation of said apparatus showing the parts of the fluid circulating system with which the present invention is concerned, other parts being omitted for the sake of clearness. Figure 3 is a detail elevation, on an enlarged scale, of a portion of the apparatus of Figure 2 for applying bleaching solution and a subsequent washing liquid tothe thread, parts of the apparatus being broken away for the sake of clearness. Figure 4 represents a flow diagram of the path The method of determining the pH of the followed by the bleaching solution and washing to advance the thread lengthwise thereof in a large number of closely spaced, genera lly helical turns. The thread I is discharged at the unsupported end of each reel, from which it passes to the succeeding reel.

The unsupported end of each reel 5 is disposed beyond the lateral edge of trough 4, thus enabling the thread I leaving the reel to pass vertically downward through channel I5 to the supported end of reel 6, the second reel of the series. The thread on reel 5 is not subjected to the action of any processing liquid other than coagulating liquid carried up to reel 5- by the thread leaving coagulating bath 3. The function of'reel 5, in addition to drawing the thread from coagulating bath 3, is to provide a period for completion of coagulation of the thread; i. e., regeneration of the cellulose content thereof.

Means are provided for applying to the thread on reels 6 to 9, inclusive, processing liquids such as those for hardening, desulfurizing, washing, etc. Reels I and II have associated therewith means for bleaching and washing the thread according to the present invention, as more fully described hereinafter. On reel I2 8. finishing liquid is applied to the thread. Reel I3 may be a drip reel on which the thread is stored for a period long enough to permit excess liquid to drip therefrom before it is passed tqdrying reel I4.

From reel I the dried thread passes directly to cap twister I6.

In the apparatus shown in the drawings, reels 5 to I 4, inclusive, are disposed in stepped arrangement with their unsupported ends extending in the same direction and with the thread-receiving end of each reel in apposite relation to the thread-discharge end of the preceding reel. Corresponding reels in adjacent downwardly extending series are disposed in horizontal series lengthwise of the machine, so that the machine as a whole comprises two inclined banks of reels disposed on opposite sides of coagulating trough I. The arrangement of reels in each bank and the arrangement of banks provide important advantages in making possible easy accessibility to the reels for operating purposes.

Each of reels 5 to I2, inclusive, has associated therewith a tube I! by means of which liquid is applied to the thread. Each of said reels is tilted so that its thread-discharge end is elevated slightly. The liquid is applied toward the threaddischarge end of the reel in such manner that it forms a film which envelops the thread on the reel. The liquid dripping from the reel is collected in a trough I8 below the reel extending beneath adjacent reels in the same horizontal series.

Distributing tubes I! for each of the liquid processing reels other than reel 6 are supplied with processing liquid from a conduit I9 formed apparatus and supplies liquid to a plurality of corresponding reels disposed in the same horizontal series. Tubes IT for reels 6 are supplied from a separate longitudinally extending conduit 2I disposed above reels 6.

Figures 2 to 4, inclusive, illustrate the system by which bleaching solution and wash water may be prepared and supplied to thread I according to the present invention.

In the preparation of a suitable sodium hypochlorite solution, water is supplied to reaction tank 25, shown diagrammatically in Figure 4, through a pipe 22. Sodium hydroxide solution; for example, a solution of approximately 19% N'aOH, is supplied from reservoir 23 through pipe 24, the solution being diluted to the desired concentration (e. g., approximately 5% NaOH) with water from pipe 22. Chlorine from container 25 is supplied through pipe 21 to reaction tank 25, where it is passed through the diluted caustic solution to form sodium hypochlorite. The volume of water, caustic and chlorine passed to reaction tank 25 is preferably so regulated by valves 28 in the respective pipes 22, 24 and 21, that the reaction is carried to a point slightly on the alkaline side.

The desired concentration is reached when approximately 0.43% NaOH, calculated as free alkali, is left in the sodium hypochlorite solution, which preferably contains about 4% NaOCl.

The temperature of the solution in reaction tank 25 is maintained throughout the reaction at a moderate level, preferably about 19 C. This may conveniently be done by .passing cooling brinefrom pipe 25 through a cooling jacket around reaction tank 25. If desired, however. watersupply pipe 22 may 'be jacketed with a cooling medium to reduce the temperature of the water added to reaction tank 25 as a diluent.

thereby obtaining a resultant low reaction temperature.

The prepared solution is withdrawn from reaction tank 25 through conduit 3I to make-up tank 52.

In the make-up tank, the excess alkali (approximately 0.43% NaOH) is neutralized by the addition of dilute hydrochloric acid from container 33 through conduit 34. The solution is adjusted to a pH of substantially 7 as determined .by the use of Bromthymol Blue as an indicator after the available chlorine has been dissipated by the addition of hydrogen peroxide. Other acids, such as sulfuric, hydrobromic, phosphoric, etc., or even strong acid salts such as sodium acid sulfate, etc., may be employed to neutralize the free alkali, hydrochloric acid being given merely as an example.

The concentration of hypochlorite solution is then adjusted from approximately 4% NaOCl to approximately 0.05% NaOCl by the addition of warm water from water-heating tank 35 through pipe 36. Water may be supplied to tank 35 from the pipe 22 supplying reaction tank 25. The temperature of the water added to make-up tank 22 is preferably such that the resulting solution will be at a temperature of approximately 30 C. when applied to thread I on reel I0. To the liquid in make-up tank 32 is also added partially spent bleaching solution returned through conduit 31 as hereinafter explained.

The bleaching solution thus prepared passes from make-up tank 32 through conduit 38 to suitable temporary storage tanks 35 from which it may be withdrawn, as by means of pumps I,

as needed by constant-head supply box 43 (Figures 2 and 3). Constant-head supply box 43 furnishes bleaching solution through feed pipes 44 to conduits II for reels i0. Supply pipe 42, associated with pumps 4|, preferably supplies more bleaching solution to constant-head supply box 43 than is passed therefrom through feed pipes 44; consequently, overflow 45 is provided in constant-head supply box 48 to permit the excess to escape through conduit .45. In this manner, the hydrostatic pressure in feed pipes 44, conduits II, and distributor tubes I1 is maintained at a substantially constant value.

As shown in Figure 3, bleaching solution passed through feed pipes 44 and conduit ll formed integrally with the forward edge of trough It below reels 9 is applied to the thread on each reel I. through its corresponding distributor tube ii. The film of liquid which forms on reel I. effects particularly eillcient treatment of the thread before the partially spent liquid drips into trough 18. Where reel ii! is 5 inches in diameter, stores about 50 meters of thread thereon, and rotates at about 170 R. P. M., it is desirable to supply the bleaching solution through each of the distributor tubes I! at the rate of approximately 250 c. c. per minute to obtain optimum results.

An aperture 41 at one end of each trough it permits the bleaching liquid collected thereby to be withdrawn by gravity from trough ll through drain pipe 48 associated therewith. Conduit 4! communicating with drain pipes 48 and with conduit 48 from overflow portion 45 of constant-head supply box 43 conducts the bleaching solution into a trap 50, which has a partition ll therein. In case of emergency. some of the liquid in trap I may pass over partition II in said trap, through pipe 51 to waste pipe 83, thence to a sewer. Ordinarily, however, the major portion of the solution from conduits 44 and 48 passes from trap I! through return pipe 31 to make-up box 32.

Due to the character of the process, the bleaching solution applied to the thread in the system hereinabove described tends to become slightly acid during the progress of the bleaching operation. Consequently, when the partially spent bleaching solution is returned to make-up tank I! through line 31, the acidity thereof is counteracted by the free alkali in the fresh hypochlorite solution added through pipe 3| from reactionoontainer 25. The fresh hypochlorite solution thus added serves to refresh the supply of available chlorine" in the bleaching solution.

Often the free alkali added with the fresh hypochlorite solution is greater than the amount necessary to neutralize the acidity of the partially spent solution. As a consequence thereof. it may be necessary to add more hydrochloric acid from container 31 and readjust the solution to a pH value of 7 as already described. Under certain circumstances. it may be necessary to add fresh caustic instead of acid to the spent solution to keep the desired pH value. In such case. caustic may be supplied directly from tank 23 through line i! to make-up tank 32.

Inasmuch as it is desirable to refresh the bleaching solution continuously with the circulation thereof, it is usually found necessary to discard a measured volume of partially spent liquid per unit of time, as by bleeding off liquid from return pipe 31 through line 40. In this manner, the volume of continuously refreshed bleaching solution, allowing for addition of water, fresh bleaching solution, evaporation and other loss of fluid, will be maintained substantially constant. The rate of discarding, and likewise the rate of addition of fresh bleaching solution, may be determined by the denier of the thread, the desired concentration of NaOCl, the temperature of the solution, etc.

The wash liquid supplied to the thread on reel H, which may be fresh water. is conducted to reel H by means similar to those hereinabove disclosed in connection with the supply of bleaching solution to the thread on reel il.

In the system illustrated, heated wash water from tank I! is supplied by pumps I4, pipe 3! and supply pipe SI to constant-head supply box 56. Feed pipes 51 conduct the water under substantially constant hydrostatic pressure from supply box I. to conduits II formed in the fOrw' ward edge of each trough I! disposed below reels II. The wash water is supplied from conduits I! through distributor pipes [1 associated with reels ii. The water supplied to reels H from tank 35 is heated, as by steam coils, to a temperature such that the wash liquid prepared therefrom, when applied to thread i, will have a temperature of approximately 30' C.

An overflow portion '8 is provided in constanthead supply box SI by which excess water supplied through pipes Ii associated with pumps 84 may pass through overflow conduit 5! to wash water trap I.

Water leaving the thread stored on reels ii is collected in another trough 18 disposed therebelow. The contaminated water passes throu h aperture 41 in said trough II to drain pipes H. A common conduit 02 communicating with the drain pipes 4| on opposite sides of the apparatus conducts the contaminated wash water to trap N. If it is found to be desirable to reuse the commingled washing liquid, for instance, on another treating stage. it may be passed from trap through pipe 3 to suitable recirculating means; otherwise, pipe I! may communicate with the sewer. In case of emergency, liquid overflowing the partition 44 in trap I passes through pipe 05 to waste pipe N to be discarded.

Valves 1 in pipes 41 and it near supply boxes 48 and It. respectively, serve to regulate the volume of liquid passed to said supply boxes.

In the continuous processing of thread. the bleaching solution is not stored for any lon p riod but is constantly recirculated, so that no substantial decomposition of the bleachin solution tends to occur in spite of the neutralization of the free alkali with a strong acid. Thorough bleaching and washing of the thread is obtained even though the thread is subjected to each of these treatments for less than a minute. This results from the fact that a relatively high ratio of liquid to thread is provided, as well as from the fact that the operations are performed at moderate temperatures.

It has been found that under such circumstances, no treatment of the thread with an antichlor is required. It is only necessary that the thread be thoroughly washed, after which it may be dried or, as in the illustrated embodiment of the invent on, be subjected to other processing treatment. Thread produced as above described is not uniformly bleached but is of high quality: despite the fact that no antichlor is applied thereto. its physical and physico-chemical characterlstics are in no way impaired.

Besides making possible the omission of the anti-chlorination step, the invention has been found to give rise to increased bleaching efficiency.

The foregoing description of the invention is illustrative merely: various modifications may be made therein without departing from the spirit of the invention. As hereinbefore indicated, other alkali or alkaline earth oxy-halogen bleaching solutions than sodium Vhypochlorite solutions may be used. Similarly, strong acid or strong acid salts other than hydrochloric acid may be used to neutralize the free alkali in the particular oxy-halogen solution employed Other changes may be made within broad limits in the procedural aspects of the invention. I

Numerous modifications may likewise be made in the apparatus; indeed, the invention may readily be practiced by means of sundry other types of processing apparatus. The invention is not restricted to the continuous processing of artificial silk thread, but may, under suitable conditions, be employed to process various other kinds of artificial threads. It may also be employed in the processing of manyfother textile materials, including those of natural origin.

It is intended that the patent shallcover, by

suitable expression in the appended claims, whatever features of patentable novelty reside in the invention.

What is claimed is:

l. The method of bleaching regenerated cellulose thread comprising continuously b'ut temporarily storing the thread in the form of an advancing helix characterized by a large number of closely spaced turns; treating the thread while in helical form with a bleaching solution con taining a strong-acid-neutralized oxy-halogen salt of a metal from the group consisting of the alkali and alkaline-earth ,metals, said solution having an available chlorine content such that the time required for bleaching the thread is less than a minute; washing the bleached thread without using an antichlor; and drying the washed thread.

2. The method of bleaching regenerated cellulose thread comprising continuously but temporarily storing the thread in the form of an advancing helix characterized by a large number of closely spaced turns; treating the thread while in helical form with a bleaching solution contalim'ng a strong-acid-neutralized oxy-halogen salt of a metal from the group consisting of the alkali and alkaline-earth metals; washing the bleached thread while in helical form without using an antichlor, the washing time being less than a minute; and drying the washed thread.

3. The method of bleaching regenerated cellulose thread comprising continuously but temporarily storing the thread in the form of an ad-- vancing helix characterized by a large number of closely spaced turns; treating the thread while in helical form with a bleaching solution containing a strong-acid-neutralized oxy-halogen salt of a metal from the group consisting of the alkali and alkaline-earth metals, said solution having an available chlorine content such that the time required for bleaching the thread is less than a minute; washing the bleached thread while in helical form without using an antichlor, the washing time being less than a minute; and drying the washed thread.

4. The method set forth in claim 1 wherein the oxy-halogen salt is sodium hypochlorite.

5. The method set forth in claim 2 wherein theoXy-halogen salt is sodium hypochlorite.

6. The method set forth in claim 3 wherein the oxy-halogen salt is sodium hypochlorite.

ALDEN H. BURKHOLDER.

CERTIFICATE} OF comma-T1011. I Patent No. 2,502,956. -November 21;, 194;.

- ALDEN H. BURKHCLDER.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 3, second column, line 70, for "not uniformly" read --not only uniformly; and

that the said Letters Patent should be read. with this correction therein that the same may conform'to the record of the case in the Patent Office. Signed and sealed this 12th day of January, A. 1). 15m.

Henry Van Arsc'lale,

(Seal) Acting Commissioner of Patents.

CERTIFICATE} OF come-T1021. Patent No. 2,502,956. -Hdvember 21;, 194 2.

- ALDEN H. BURKHOLDER.-

It is hereby certified thet error appears in the printed speeiflcation of the above numbered patent requiring correctionas follows: Page 5, second colu mn, line 70, for "not uniformly read --not only unifomly--; and that the said Letters Patent should be read with this correction therein that the same may conform "to the record of the case in the Patent Office.

Signed and sealed this 12th dayef January, A. n. 1515.

. Henry Van Aredale; (Seal) I Acting Commissioner ef Patents. 

